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Communication between median and musculocutaneous nerve
Sachdeva, K.1* and Singla, RK.2
1
Anatomy Department, Chintpurni Medical College, Bungal, Pathankot, Índia
Anatomy Department, Government Medical College, Amritsar, Punjab, Índia
*E-mail: [email protected]
2
Resumo
Neural variations of the brachium constitute an important anatomical and clinical entity. Although frequently
reported, if accompanied by other anomalies, they deserve special mention in anatomical literature. The nerves
of the extremities are especially vulnerable to injury because of their long course and superficial distribution.
The variations of the median nerve and the musculocutaneous nerve, like the communication between the
two, may prove valuable in the traumatology of the shoulder joint. It may also be correlated to the entrapment
syndromes of the musculocutaneous nerve in which a part of the median nerve also passes through the
coracobrachialis and may exhibit the symptoms similar to those encountered in the median nerve neuropathy
as in the carpal tunnel syndrome. In the present case, in the right upper limb of a 60 year old male, the
musculocutaneous nerve after its origin from lateral cord gave a branch to corachobrachialis muscle and then
fused completely with median nerve. Later then supplied the other two muscles of the front of forearm, i.e.
biceps brachii and brachialis and the lateral cutaneous nerve of arm. Its ontogeny, phylogeny and clinical
implications are discussed in detail. A lack of awareness of variations with different patterns might complicate
surgical repair and may cause ineffective nerve blockade.
Keywords: brachial plexus, communication, median nerve, musculocutaneous Nerve.
1 Introduction
Variations in the formation and branching pattern of
the brachial plexus constitute an important anatomical and
clinical entity and have been reported by several investigators
(KERR, 1918; MILLER, 1934; BERGMAN, AFIFI and
MIYAUCHIR, 1988). The median, musculocutaneous
and ulnar nerves after their origin from the brachial plexus,
pass through the anterior compartment of the arm without
receiving any branch from any nerve in the neighbourhood
(HOLLINSHEAD, 1976). Although the communications
between the different nerves in the arm are rare, those
between the median nerve (MN) and musculocutaneous
nerve (MCN) have been described from nineteenth century
(HARRIS, 1904). Knowledge of anatomical variation of
these nerves at the level of upper arm is essential in light of
the frequency with which surgery is performed in the axilla
and the surgical neck of the humerus (LEFFERT, 1985).
One such case was found in the Department of Anatomy,
Government Medical College, Amritsar, Punjab, India;
where a communication was seen between MN and MCN in
the right arm of a 60 year old adult male cadaver.
2 Case report
During routine undergraduate dissection, in the right
upper limb of a 60 year old adult male cadaver, the MCN
arose normally from the lateral cord of brachial plexus. The
MN was formed by the union of a lateral root coming from
lateral cord and a medial root coming from medial cord, in
front of the third part of axillary artery. The MCN as a whole
did not pierce corachobrachialis but instead gave a branch to
it which entered the corachobrachialis muscle. After this, the
MCN, ran downwards and medially for about 4 cm, crossed
the third part of axillary artery and joined the MN, 3.5 cm
246
after its formation. The other two muscles of the front of the
arm viz. biceps brachii and brachialis were supplied by the
median nerve after it received the musculocutaneous nerve.
Similarly the lateral cutaneous nerve of arm also emerged
from median nerve (Figure 1 and 2).
3 Discussion
Anastomosis between the MCN and the MN is by far
the most common and frequent of all the variations that
are observed among the branches of the brachial plexus
(VENIERATOS and ANANGNOSTOPOULOU, 1998).
Table 1 depicts the incidence of communication between
musculocutaneous nerve and median nerve irrespective of
its site or type as reported earlier from time to time. It is seen
to vary between a wide ranges of 1.4% to 63.5%.
The communication between the MCN and the MN
have been classified in different types by Li Minor (1992),
Venieratos and Anagnostopoulou (1998) and Choi et al.
(2002).
Li Minor (1992) categorized these communications into
following five type: In type I, there is no communication
between the MN and the MCN, in type II, the fibers of the
lateral root of the MN pass through the MCN nerve and join
the MN in the middle of the arm, whereas in type III, the
lateral root fibers of the MN pass along the MCN and after
some distance, leave it to form the lateral root of the MN. In
type IV, the MCN fibers join the lateral root of the MN and
after some distance the MCN arises from the MN. In type V,
the MCN is absent and the entire fibers of the MCN pass
through the lateral root and fibers to the muscles supplied by
MCN branch out directly from the MN (Figure 3).
J. Morphol. Sci., 2011, vol. 28, no. 4, p. 246-249
Communication median and musculocutaneous nerves
LC
MC
LRM
MCN
MRM
BrCbr
MN
Br
BB
LCNA
Figure 1. Line diagram showing communication between
Median Nerve and Musculocutaneous Nerve in the present case.
LC- Lateral Cord, LRM-Lateral Root of Median Nerve, MRMMedial Root of Median Nerve, MN- Median Nerve, MCNMusculocutaneous Nerve, BrCbr-Branch to Corachobrachialis,
Br- Branch to Brachialis Muscle, BB-Branch to Biceps Brachii,
LCNA-Lateral cutaneous Nerve of Arm.
Br of MCN to CBr
LRM
Brs to BB & Br
Muscles from MN
Lateral cord
Communication MCN
between MN & MCN
MN
MRM
AA
3.1 Ontogeny
Medial cord
UN
Figure 2. Observe the communication between the
musculocutaneous nerve and the median nerve. MN: median
nerve; MRM: medial root of median nerve; LRM: lateral root
of median nerve; UN: ulnar nerve; MCN: musculocutaneous
nerve; AA: axillary artery; BB: biceps brachii muscle; Br: bracialis
muscle; CBr: corachobrachialis muscle; Brs: branches.
Similarly based upon its site with relation to the
coracobrachialis muscle Venierators and Anagnostopoulou
(2000) classified this communication into three types. In
type I, communication between MCN and MN is proximal
to the entrance of the MCN into the coracobrachialis,
whereas in type II, the communication is distal to the muscle
J. Morphol. Sci., 2011, vol. 28, no. 4, p. 246-249
and in type III neither the nerve nor its communicating
branch pierces the muscle.
Later on Choi et al. (2002) in a study on 138 cadavers
classified these communications into three types. The
first pattern comprised of fusion of both nerves (19.2%).
Pattern 2 showed the presence of one supplementary
branch between both nerves (72.6%). This type was further
subdivided as Pattern 2a, where a single root from MCN,
contributes to the connection (69.9%) while in Pattern 2b
there are two roots from MCN (2.7%). Pattern 3 showed
presence of two branches between both nerves (6.8%).
Connection between the MCN and MN in the present
study could not be incorporated exactly into any of the types
described by Li Minor (1992). However it fits into type II of
Venieratos and Anagnostopoulou (1998) or into type II (2a)
of Choi et al. (2002).
The most frequent variation is the presence of a
communicating branch that emerges from the MCN
and goes distally to join the MN, an anastomosis
observed in the lower third of arm (VENIERATOS and
ANANGNOSTOPOULOU, 1998; BERGMAN, AFIFI
and MIYAUCHIR, 1988). If this branch is given off in
upper third of the arm, it is generally considered as third
(double lateral) root of the median nerve (BERGMAN,
AFIFI and MIYAUCHIR, 1988). In the present case, the
musculocutaneous nerve in upper third of the arm, passed
medially downwards and joined the MN. It can be considered
as the double lateral root of the MN or in other words the
MN nerve can be said to be formed by three roots: a) one
from the lateral cord; b) one from the MCN; c) and the third
from the medial cord.
Similar variation was observed earlier by different authors
- The median nerve, instead of having two roots may have
three roots - either one each from lateral cord, medial cord
and MCN (CHAUHAN and ROY, 2002; SARITHA, 2004)
or two from lateral cord and one from the medial cord
(MOHAPATRA et al., 2004) or it may have even four roots
– three from the lateral cord and one from the medial cord
(UZUN and SEELIG, 2001).
The presence of such communications may be attributed
to random factors influencing the mechanism of formation
of limb muscles and the peripheral nerves during embryonic
life. Significant variations in nerve patterns may be a
result of altered signaling between mesenchymal cells and
neuronal growth cones (ABHAYA, BHARDWAJ and
PRAKASH, 2003) or circulatory factors at the time of
fusion of brachial plexus cords (KOSUGI, MORTIA and
YAMASHITA, 1986).
Iwata (1960) believed that the human brachial plexus
appears as a single radicular cone in the upper limb bud,
which divides longitudinally into ventral and the dorsal
segments. The ventral segments give roots to the median
and the ulnar nerves with musculocutaneous nerve arising
from the median nerve. He further kept the possibility of
failure of the differentiation as a cause for some of the fibers
taking an aberrant course as a communicating branch.
Chiarapattanakom et al. (1998) are of the opinion that
the limb muscles develop from the mesenchyme of local
origin, while axons of spinal nerves grow distally to reach the
muscles and/or skin. They blamed the lack of coordination
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Sachdeva, K. and Singla, RK
Table 1. Showing the incidence of communication between the musculocutaneous nerve and the median nerve.
Sr. no.
1
2
3
4
5
6
7
Author
Watanabe et al.
Kosugi, Mortia and Yamashita
Venieratos and Anagnostopoulou
Choi et al.
Loukas and Aqueelah
Guerri-Guttenberg and Ingolotti
Maeda et al.
II
I
LF
LF
MF
LR
Year
1985
1986
1998
2002
2008
2009
2009
MF
LF
MF
LR
LR
MR
MR
BB
B
B
B
MC M U
V
MR
CB
BB
BB
LF
MF
MR
CB
CB
LF
LR
MR
IV
III
MF
Incidence (%)
01.4
21.8
13.9
26.4
63.5
53.6
41.5
MC M U
LR
CB
CB
BB
MC M U
BB
B
B
MC M
U
M U
Figure 3. Li Minor classification of communication between musculocutaneous and median nerve (Type I to V). LF: Lateral cord;
MF: Medial cord; MC: Musculocutaneous nerve; M: Median nerve; U: Ulnar nerve; CB: Coracobrachialis muscle; BB: Biceps
brachii muscle; B: Brachialis muscle.
between the formation of the limb muscles and their
innervation for appearance of a communicating branch.
3.2 Phylogeny
Chauhan and Roy (2002) strongly recommend the
consideration of the phylogeny and the development of
the nerves of the upper limb for the interpretation of the
nerve anomalies of the arm. Considering the communication
between the musculocutaneous and the median nerve as a
remnant from the phylogenetic or comparative anatomical
point of view and that the ontogeny recapitulates the
phylogeny, they feel that the variations seen are the result of
the developmental anomaly.
Studies of comparative anatomy have observed the
existence of such connections in monkeys and in some apes;
the connections may represent the primitive nerve supply of
the anterior arm muscles (MILLER, 1934).
3.3 Clinical significance
The anatomical variation described here has practical
implications, since injury to the median nerve in the axilla
or arm would, in this case, have caused unexpected paresis
or paralysis of the flexor musculature of the el­
bow and
hypoesthesia of the lateral surface of the forearm, in addition
to the classical signs that are already well known. Injury to
the median nerve could occur in cases of open or closed
trauma to the arm, such as bullet and blade wounds or during
surgeries on the axilla or arm. The median nerve and its
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roots are close to the axillary vein, which is used as the most
cranial limit for axillary lymph node dissection, a procedure
used in treat­ing certain tumors, such as breast carcinoma
and melanoma. If the dissection extends more cranially than
normal, injury to the median nerve (or to its medial root)
may occur, with consequent dysfunction of the flexor muscu­
lature of the elbow if the anatomical varia­tion described here
is present. It would not be unlikely for such ac­cidents to
occur even with the most eminent surgeons, considering
that the classical con­cept is that the median nerve does not
give rise to branches in the arm (FREGNANI et al., 2008).
The clinical relevance of such variations might also
be correlated to entrapment syndromes. Entrapment of
MCN is rare and has its origin either in physical activity
(FALSENTHAL et al., 1984) or in violent passive movements
of arm and forearm (KIM and GOODRICH, 1984). This
knowledge may prove useful for clinicians in order to avoid
an unnecessary Carpal tunnel release (VENIERATOS and
ANAGNOSTOPOULOU, 1998).
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Received January 19, 2011
Accepted October 18, 2011
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